This invention relates to a pneumatic radial ply tire and, in particular, a radial tire suitable for use for a truck, bus, light truck, and other vehicles. It is intended for providing an improved radial tire, in which various requirements for this kind of a tire such as resistance to cutting, resistance to wear, durability to high speed running, low fuel consumption, and vehicle driving stability are well-balanced with each other and also with general characteristics indispensable for the tire such as comfortableness in vehicle riding and traction capacity without affecting these characteristics, while optimizing a radius of curvature of the radially expansive groundcontacting surface of the tread and cut grooves formed in the direction of the tire axis on its shoulder parts.
The main points of the prior art for achieving improvement in this resistance of tire to wear and cutting, durability to high speed running, and saving of fuel consumption have been such mean as the use of rubber highly resistant to wear and cutting for the ground contacting part of the tread preparation of rubber material low in gripping performance and high in repulsive resilience, or employment of a tread small in gauge, however, there have been fatal problems in that these means are all antinomic to each other because a tire designed to weigh heavily in resistance to wear and long life is insufficient in durability to high speed running and in fuel consumption and, on the contrary, a tire weighted in durability to high speed running and low fuel consumption is inevitably followed by short life because of fast wear.